lego_rc.py

import pigpio
from time import sleep

class LEGO_RC:
    """ Implements the protocol documented in LEGO Power Functions RC 1.20. """
    # https://github.com/iConor/lego-lirc/blob/master/docs/LEGO_Power_Functions_RC_v120.pdf

    def _init_waves(self, pi, gpio_pin):
        pi.wave_clear()

        def _gen_pulses(total_length_us):
            # Length of a 38 kHz cycle ~= 26.316 us.
            # Round the mark pulse lengths to 13 us and pad with accurate pause length in the end. Hope it works.
            for i in range(6):
                yield pigpio.pulse(1 << gpio_pin, 0, 13)
                yield pigpio.pulse(0, 1 << gpio_pin, 13 if i < 5 else total_length_us - (13 * 11))

        pi.wave_add_generic(list(_gen_pulses(421)))
        self._low_bit = pi.wave_create()

        pi.wave_add_generic(list(_gen_pulses(711)))
        self._high_bit = pi.wave_create()

        pi.wave_add_generic(list(_gen_pulses(1184)))
        self._start_bit = pi.wave_create()

        self._stop_bit = self._start_bit  # also 1184 us

    def __init__(self, pi, gpio_pin):
        self._pi = pi
        self._gpio_pin = gpio_pin
        self._init_waves(self._pi, self._gpio_pin)

    def _send(self, nibble1, nibble2, nibble3):
        self._pi.set_mode(self._gpio_pin, pigpio.OUTPUT)

        def _gen_waves(nibble):
            for i in range(3, -1, -1):
                yield self._high_bit if nibble & (1 << i) else self._low_bit

        lrc = 0xF ^ nibble1 ^ nibble2 ^ nibble3

        chain = ([self._start_bit] +
            list(_gen_waves(nibble1)) +
            list(_gen_waves(nibble2)) +
            list(_gen_waves(nibble3)) +
            list(_gen_waves(lrc)) +
            [self._stop_bit])
        print('wave_chain(' + repr(chain) + '):', repr(self._pi.wave_chain(chain)))

        print('Sending', end='...')
        while self._pi.wave_tx_busy():
            sleep(.01)
        print(' done')

    def drive(self, channel, speed):
        """ Combo PWM mode """
        self._send(0b0100 | channel, speed, speed)